Expression of Leptin Receptor Isoforms in vitro : Lack of Effects of Leptin on Endometrial Cytokine and MMP Production

PROBLEM

Leptin has a key role to play in human female reproduction. Its receptor is expressed highly throughout the reproductive tract. Cytokines have an important role in preparing the endometrium for implantation and leptin is known to modulate cytokine production in other tissues. We, therefore, investigated the possible role of leptin in endometrial growth and function.

METHOD OF STUDY

Reverse transcriptase polymerase chain reaction and immunocytochemistry were used to determine the pattern of expression of leptin receptor isoforms in primary human endometrial epithelial and stromal cells in culture. The effect of leptin on cell growth and on the production of cytokines [Leukaemia Inhibitory Factor (LIF), interleukin 6 and tumour necrosis factor-alpha] and matrix metalloproteinases (MMP) (MMP2 and MMP-9) was also investigated.

RESULTS

Expression of the long form of the leptin was restricted to the cultured endometrial, epithelial cells. Both cultured endometrial stromal and epithelial cells expressed the short and variant isoforms of the receptor. Incubation of epithelial and stromal cell cultures with varying concentrations of leptin (0-1000 ng/mL) had no significant effect on cell growth or levels of MMP-2 or MMP-9 production. Leptin also had no significant effect on cytokine production by epithelial cells.

CONCLUSIONS

This study shows for the first time, the presence of leptin receptor isoforms on endometrial, epithelial and stromal cells in culture. Leptin had no effect on cytokine and MMP production by these cells. However, it is possible that leptin affects other factors within the endometrium not investigated here.

A review of immune cells and molecules in women with recurrent miscarriage

Immunological rejection of the fetus due to recognition of paternal antigens by the maternal immune system, resulting in abnormal immune cells and cytokine production, is postulated to be one cause of unexplained pregnancy loss. Although there is evidence for this in rodents, there is less evidence in humans. This article focuses on studies in humans, and reviews the recent literature on the differences in immune cells and molecules in normal fertile women and women with recurrent miscarriage (RM). Although much of the evidence is contradictory, these studies do suggest differences in the expression of some immune cells and molecules in women with RM. Differences in the CD56+ population of cells are seen, and there is some evidence for an alteration in the ratio of Th1 and Th2 cytokines produced by peripheral blood monocytes (PBMCs) and clones of decidual CD4+ cells. There is also some evidence for differences in endometrial cytokine production, and in particular decreased production of pro-inflammatory cytokines such as interleukin-6. Possible reasons for the variations in data are discussed, and the importance of compartment (peripheral blood, endometrium or decidua) in which the cells and molecules are measured and the timing of the sampling, both with respect to the menstrual cycle and pregnancy (at the time or just after miscarriage) is emphasized.

Expression of interleukin (IL)-11 receptor by the human endometrium in vivo and effects of IL-11, IL-6 and LIF on the production of MMP and cytokines by human endometrial cells in vitro

Interleukin (IL)-6, leukaemia inhibitory factor (LIF) and IL-11 belong to the same family of cytokines whose receptors utilize gp130 as the signalling molecule. We have investigated the expression of the IL-11 receptor, IL-11Ralpha, protein in the human endometrium in vivo and the effects of IL-6, LIF and IL-11 on the production of metalloproteinases (MMPs) and cytokines by cultured endometrial epithelial and stromal cells. Immunostaining showed that IL-11Ralpha was expressed in both epithelial and stromal cells, with epithelial staining being more intense than stromal staining and little variation in staining in either compartment throughout the cycle. Incubation of both stromal and epithelial cells with IL-6, LIF and IL-11 had no effect on MMP-2, -7, -9, transforming growth factor (TGF)beta or IL-1beta production or cell growth. IL-6 and LIF also had no effect on tumour necrosis factor (TNF)alpha production, but IL-11 caused a dose-dependent decrease in TNFalpha production by epithelial cells. IL-6 receptor, LIF receptor and gp130 were all expressed by cultured stromal and epithelial cells, showing that the lack of effect is not due to lack of expression of the receptor components. The results show that although IL-6, LIF and IL-11 signal through the same molecule, they may have different effects in endometrial cells, suggesting the activation of different signalling pathways, which may ultimately be important in the control of endometrial function.

Interleukin-11 (IL-11) in human endometrium: expression throughout the menstrual cycle and the effects of cytokines on endometrial IL-11 production in vitro

Interleukin-11 is a member of the IL-6 family of cytokines. Its presence in mouse decidua has been shown and experiments in genetically modified mice have suggested the importance of its receptor in stromal cell decidualization. In this study we used immunocytochemistry to determine expression of IL-11 in human endometrium. The effects of TNFalpha, IL-1alpha and TGFbeta on IL-11 production by epithelial and stromal cells was also investigated. Immunocytochemical staining in sections cut from 19 endometrial biopsies obtained throughout the menstrual cycle showed that IL-11 was expressed in both human endometrial epithelial and stromal cells, with epithelial staining being more intense than that seen in the stromal cells, at all times except the late secretory phase when the intensity was similar. Basal IL-11 production by cultured epithelial cells was greater than basal production by stromal cells. IL-1alpha, TNFalpha and TGFbeta (0.1-10 ng/ml) all caused a concentration-dependent increase in IL-11 production by both epithelial and stromal cells, but stimulated: basal values were greater for stromal than epithelial cells for all three cytokines. This work shows, for the first time, the presence of IL-11 within the human endometrium and that its production is controlled by other cytokines, which are postulated to play a role in implantation. Thus IL-11 may also play an important role in human endometrial function and embryo implantation.

Expression of nuclear factor kappa B in human endometrium; role in the control of interleukin 6 and leukaemia inhibitory factor production

Expression of the rel-A component of nuclear factor kappa B (NFkappaB) by human endometrial cells was investigated by immunocytochemical analysis of cryostat sections cut from endometrial biopsy material and of cultured endometrial epithelial cells. In-vivo expression of rel-A was low in epithelial cells in endometrium obtained during the proliferative phase of the cycle, but increased in these cells during the secretory phase and was maximal at the time of implantation. In-vivo expression of rel-A by stromal cells did not vary greatly throughout the cycle, but showed a slight peak at the time of ovulation. In contrast similar expression of rel-A was seen in short-term cultures of epithelial cells prepared from both proliferative and secretory endometrium. Addition of the NFkappaB inhibitor SN50 (5 microg/ml) to confluent cultures of endometrial epithelial cells inhibited interleukin (IL)-1alpha (10 ng/ml) and tumour necrosis factor alpha (TNFalpha) (10 ng/ml) stimulated IL-6 (P < 0.001 and P < 0.01 respectively) and LIF (P < 0.01 and P < 0.05 respectively) production. The proteasome inhibitor MG132 (0.3 and 3 micromol/l) also caused a dose-dependent decrease in IL-1alpha and TNFalpha-stimulated IL-6 (P < 0.001 and P < 0.001 respectively) and leukaemia inhibitory factor (LIF) (P < 0. 001 and P < 0.001 respectively) production by endometrial epithelial cells. The results support the hypothesis that NFkappaB mediates signalling between IL-1 and TNFalpha receptors and the expression of LIF and IL-6 in endometrial epithelial cells.